Electrical leads for cryogenic devices

ABSTRACT

Heat which is conducted into the cryogenic environment of a cryogenic liquid or gas along an electrical lead of a device immersed therein is shunted into a stack of perforated plates, each spaced from adjacent plates by insulating separators, and each of which is conductively connected by a respective tap to the lead. Vapor evaporated from the bath is passed through the plates which absorb the heat that would otherwise pass through the lead into the bath, thereby reducing the boil-off of liquid from the bath.

llnfited States Fleming et a1.

[54] ELECTRHCAL LEADS FOR CRYOGENIC DEVICES [72] Inventors: Robert B.Fleming, Scotia; Carl B. Rosner,

Schenectady, both of NY.

[73] Assignee: General Electric Company [22] Filed: Dec. 15, 1969 [21]Appl. No.: 885,225

[58] Field of Search ..62/54, 514; 174/15; 165/164, 165/185; 338/51, 52

[56] References Cited UNITED STATES PATENTS 2,958,021 10/1960 Cornelisonet al ..l74/l5 mingle [4 1 Apr..4,1972

Latham 1 74/1 5 Camille, Jr 174/15 Primary Examiner-Meyer PerlinAssistant Examiner-Ronald C. Capossela Attorney-Paul A. Frank, John F.Ahern, Julius J. Zaskalicky, Frank L. Neuhauser, Oscar B. Waddell andJoseph B. Forman [5 7] ABSTRACT 6 Claims, 3 Drawing Figures PATENTEDAPR4 I972 3, 654, 377

2a I Z4 Inventors: Paberz: B. F/em/h The/r7 Aborny ll ELECTRICAL LEADSFOR CRYOGENIC DEVICES The present invention relates to electrical leadsfor conducting current from a warm region to a cold region and, moreparticularly, to such leads for conducting large currents to cryogenicdevices immersed in a cryogenic medium.

Liquid helium is used to cool most devices operating near 4K. In thecase of superconducting solenoids, large currents must generally beconducted from a power supply at room temperature to the liquid helium.The current carrying conductors must have a large cross-sectional areain order to avoid resistive losses. However, such large cross-sectionalarea allows high thermal conduction into the liquid helium. Theconsequent high rate of helium boil off is wasteful. The boiled offhelium vapor possesses a large capacity for cooling. The presentinvention is directed to means associated with the electrical lead-inconductors to the helium bath to inhibit the boil off of helium and makeeffective use of the cooling capacity of the boiled off helium.

Accordingly, it is an object of the vide improvements in electrical thecharacter described.

Another object of the present invention is to provide a simple andcompact lead structure of the character described.

It is another object of the present invention to provide an electricallead of the character described having high conduction for electricalcurrents and having low conductivity for heat flow from the warm to thecold end thereof.

It is another object of the present invention to provide a currentconducting lead for cryogenic devices which has low resistance to gasflow from one end to the other end thereof.

It is a further object of the present invention to provide a cryogeniclead construction which is highly efficient in the exchange of heatbetween the electrical conduction portion thereof and the fluid flowingin the heat exchanger portion thereof.

' In accordance with an illustrative embodiment of the presentinvention, there is provided a plurality of high conductivity porousplates and a plurality of low conductivity separators. Each separator isinterposed between and in contact with adjacent ones of the plates andeach of the separators has an enclosing rim portion. The spacers in theplates are aligned to form a longitudinal channel for the passage offluid therethrough. The plates are situated adjacent to an elongatedelectrical lead with the plates being perpendicular to the longitudinalaxis of the lead. A plurality of tabs are provided, each tabconductivity connected between a respective plate and an adjacent pointon the lead.

The novel features which are believed to be characteristic of thepresent invention are set forth in the appended claims. The inventionitself, however, together with further objects and advantages thereofmay best be understood by reference to the following description takenin connection with the accompanying drawings wherein:

FIG. 1 is a side view in section of a dewar flask into which current isconducted through electrical leads in accordance with the presentinvention.

FIG. 2 is a top view of the dewar flask and leads of FIG. 1.

FIG. 3 is a perspective view of a portion of the lead structure ofFIGS.l and 2.

Referring now to FIGS. 1 and 2 there is shown a dewar containing acryogenic liquid 11, such as, for example, liquid helium. Immersed inthe cryogenic liquid is an electrically operated device 12 intended tobe operated at cryogenic temperatures, that is, the temperature of, forexample, liquid helium, hydrogen, neon, nitrogen, argon or oxygen. Theelectrical device may be a device such as a motor, gryoscope, coil andthe like requiring electrical current for its operation. Also shown area pair of electrical lead assemblies 13 and 14 in accordance with thepresent invention. Each of the lead assemblies l3 and 14 are identicalin structure and are sealed and supported in an insulating cover 15 forthe dewar and extend present invention to procurrent conduction leads offrom a region inside the dewar adjacent the liquid 11 to a regionexternal or outside the dewar. The electrical lead assembly 13 includesa current conducting portion 20 and a heat exchanger portion 21conductively connected to the electrical current conducting portionalong the length thereof. Similarly, the electrical lead assembly 14includes an electrical lead portion 22 and a heat exchanger portion 23conductively connected to the electrical current carrying portion alongthe length thereof. One terminal of the electrical load 12 is con nectedthrough the electric current conductor portion 20 to one terminal 24 ofa source 25 of electrical current, such as a battery, and the otherterminal of the load 12 is connected through the current carryingportion to the other terminal 26 of the source 25.

Reference is now made to FIG. 3 which shows a perspective view of theconstruction of the lead assemblies 13 and 14. The current carryingportion of each of the electrical lead assemblies l3 and 14 is anelongated electrical lead 30 having a longitudinal axis. The heatexchanger portion 31 of the assemblies l3 and 14 includes a plurality ofidentical high conductivity porous plates 32 and a plurality of lowconductivity separators or spacers 33. The plates may be made ofaluminum or copper and the separators or spacers may be made of aninsulating material such as a plastic. Each of plates 32 has a centralcircular portion in which are formed a plurality of small holes orperforations 34 extending from one face of the plate to the oppositeface and having a rim or peripheral portion 35 which is nonporous. Eachof separators 33 is annular in form and is of a size to bear against thenonporous portions 35 of adjacent plates. Portions 35 are nonporous toprovide good heat conductivity therealong. Each separator 33 isinterposed between and in contact with the nonporous portions ofadjacent ones of the plates 32. Accordingly, the stacking of the platesand separators forms a longitudinal channel having an axis parallel tothe normals to the plates. The peripheral or rim portions of the plates32 are spaced adjacent to the electrical conductor 30 with the axis ofthe channel parallel to the longitudinal axis of the conductor 30.Conductive tabs 36 are provided on each of the plates connecting arespective conductive peripheral or rim portion of a plate to anadjacent area on the electrical conductor 30. The tabs may be soldered,welded or brazed to the electrical conductor. The plates 32 and theelectrical conductor 30 may be made of aluminum or copper. The tabs areprovided with sufficient crosssectional area to provide good heatconduction from the electrical conductor 30 to the heat exchanger 31.The plates 32 and the plastic spacers 33 may be bonded by epoxy to formgood seal. If desired, the external surface of the heat exchangerassembly 31 as well as the conductor 30 may be provided with a clothreinforced plastic coating 37 to provide electrical insulation of thelead assembly. The tabs 36 are made sufficiently flexible to permitdifferential contraction between the conductor 30 and the stack ofplates 32. Preferably, alternate porous or perforated plates in eachlead assembly are provided with perforated holes which are misalignedwith the perforated holes of an adjacent plate to provide a tortuouspath for fluid flowing in the heat exchanger for good heat transfer.

The parallel plate construction of the assembly provides a simple andcompact heat exchanger connected to a lead for efficiently utilizing thecooling capacity of cryogenic fluid evaporated from the bath. Theassembly of the present invention provides low pressure drop from thevapor inlet to the vapor exit end while at the same time provides ahighly effective heat exchanger due to the high surface to volume ratioof the heat exchanger portion and the arrangement of the holes in theplates. The rim portions of the plates are made sufficiently large toenable rapid conduction of heat therethrough. The circular geometry ofthe assembly provides minimal external surface area in relation tochannel volume to provide efficient conduction of heat from theelectrical conductor to the heat exchanger channel.

We intend by the appended claims to cover all modifications that fallwithin the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In combination,

an elongated electrical lead having a longitudinal axis,

a plurality of high conductivity porous plates,

a plurality of low conductivity separators, each separator interposedbetween and in contact with adjacent ones of said plates, each of saidplates having an enclosing rim portion, said separators and said platesbeing aligned to form a longitudinal channel for the passage of fluidtherethrough,

said plates being situated adjacent to said lead with the said platesbeing perpendicular to the longitudinal axis of said lead, and

means for conductively connecting each of said plates to said lead.

2. The combination of claim 1 in which said connecting means includes aplurality of tabs, each tab conductively connected between a respectiveplate and an adjacent point on said lead.

3. The combination of claim 2 in which said porous plates are plateshaving a multiplicity of holes with parallel axes.

4. The combination of claim 3 in which the holes in one plate arenonaligned with the axes of the holes in an adjacent late. p 5. Thecombination of claim 1 in which each of said separators is annular inoutline and in which each of said plates is circular in outline.

6. The combination of claim 1 in which the region of each of said platesincluded between the adjacent separators is nonporous.

1. In combination, an elongated electrical lead having a longitudinalaxis, a plurality of high conductivity porous plates, a plurality of lowconductivity separators, each separator interposed between and incontact with adjacent ones of said plates, each of said plates having anenclosing rim portion, said separators and said plates being aligned toform a longitudinal channel for the passage of fluid therethrough, saidplates being situated adjacent to said lead with the said plates beingperpendicular to the longitudinal axis of said lead, and means forconductively connecting each of said plates to said lead.
 2. Thecombination of claim 1 in which said connecting means includes aplurality of tabs, each tab conductively connected between a respectiveplate and an adjacent point on said lead.
 3. The combination of claim 2in which said porous plates are plates having a multiplicity of holeswith parallel axes.
 4. The combination of claim 3 in which the holes inone plate are nonaligned with the axes of the holes in an adjacentplate.
 5. The combination of claim 1 in which each of said separators isannular in outline and in which each of said plates is circular inoutline.
 6. The combination of claim 1 in which the region of each ofsaid plates included between the adjacent separators is nonporous.